What is the purpose of using cobalt glass?

Cobalt glass, also known as smalt, is known primarily as decorative glass with a deep blue color. It is also used as a colored lens to filter out yellow pigment.

The earliest known cobalt glass is dated at 2,000 B.C. It is then seen 500 years later as pigment in Egyptian pottery and heavily throughout ancient Chinese porcelain from 1,122-221 B.C. Cobalt was once used as pigment for paint, but it was found it faded too quickly. Other uses for cobalt include powerful magnets, high-temperature high-speed cutting tools, radiation food sterilization, radiation therapy and electroplating. It was named by German miners who attributed it to mischievous spirits called kobalds.